Like Wekemple, I'd like to know how you do it....single handed, 30 mph or kts, crosswind, 38 foot boat, fin keel? My boat is smaller....I can't do it. A bigger boat is harder to handle. Backing a fin keel boat from essentially dead in the water into 30 kts.? I think what is going to happen is that the wind is going to take charge, the prop walk is going to walk stern around to one side regardless of where the rudder is, the wind will then catch the boat and spin you around out of control, and probably down on adjacent boats or piers. If you are already backing at good speed and then turn upwind, you may be able to back against the wind, but this is not what you have when leaving the dock. If there is any wave action, the waves will be hitting the broad stern hard, trying to kill whatever stern way you have. But from standing still, I don't think you can back upwind in 30 kts. And you'll have similar challenges going ahead in such crosswinds from a standstill position, but assuming you have sufficient open water, you'll be able to regain control easier going forward because of rudder position relative to prop wash. I also use long lines to tend my bow, but in 30 kts. crosswind, I can't hold it....of course, you can snub the lines on a winch or cleat and perhaps overcome that hurtle. With my boat, and I suspect with boats in 38-40 ft. range, that crosswind is going to sweep you down on the leeward finger pier, piling, or adjacent boat in an instant. To me, at least, dragging the boat down against the pier is unacceptable and seems a good way to damage something.
I'm a fair weather sailer, probably not very good, even after many years. But at my marina, there are people who have crossed oceans, and lived the long range cruising life for years. And they don't go when the wind is blowing 30 kts., crosswind at the "dock". I hear lots of people say they go out in such conditions, but usually, I find that the pier where the boat is berthed is sheltered from such winds. But if you really have 30 kts. crosswind at the pier, maybe it's best to sail another day.
And if you get away, then there's the problem of docking in the same 30 kt. crosswind, which will be equally challenging, maybe more so.
Not trying to pick a fight, or cause trouble, but I don't believe it is done in real life. I've looked for videos showing docking/undocking in such conditions. I have yet to see one, even with all the schools and "YouTube" photographers. Can anyone point me to such videos? And if it is done, I'd really like to see it....I could learn a lot.